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Patented Feb. 19, 1929.

UNITED STATES PATENT OFFICE.

LINN BRADLEY, 0F MONTCLAIR, NEW JERSEY, AND EDYVARD P. MCKEEFE, OF PLATTS- BURGI-I, NEW YORK, ASSIGNORS TO BRADLEY-MC'KEEFE CORPORATION, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TREATMENT OF RESIDUAL LIQUOR.

No Drawing. Application filed. March 2, 1925, Serial No. 12,761, and in Canada February 9, 1922. Renewed May 11, 1927.

This invention relates to the treatment ol the residual liquors from the production of wood pulp with a cooking liquor containing sodium monosullite, or a mixture of sodium monosullite and caustic soda.

In certain companion applications we have described new and useful method of producing wood pulp from wood by subjecting the wood to a cooking operation, under pres sure and at an elevated temperature, with a cooking liquor consisting essentially of sodium monosulfite, or sodium monosullite together with a limited amount of caustic soda. Such processes result inthe production of increased yields of a superior and improved pulp, containing fibers of great strength, which have not been objectionably injured by the cooking operation.

The present invention relates to the treatment of the residual liquors from such processes, whereby the processes may be made regenerative or cyclic in character.

The residual liquors produced by such pulp processes are of distinctive and characteristic composition. They contain a decreased content. of organic matter, as compared with the black liquor from the soda or sulfate process. due to the fact that incrusting and non-fibrous constituents are dissolved or re moved from the wood without dissolving or removing; any considerable amount oi? the iibcrs themselves, whereas, in the soda and sulfate processes, a considerable amount of the libers dissolved and goes into the rcsidual liquor.

The composition of the residual liquors which are treated according to the present invention will vary somewhat with dillcrent woods, and with the particular composition of the cooking liquor. With deciduous woods, such poplar, basswood, maple, birch, beech, oak, etc, and with certain coniferous woods, such as spruce. pines, etc. the cooking operation may be carried out with a cooking liquor containing essentially normal sodium sullite. lVith other woods, particularly highly resinous woods, such as certain pines, the cooking, liquor may contain a su'li'icient amount of caustic soda, in ad.- dition to a prepomlerating proportion of sodium sulti to, so that the resinous and other inc-rusting and non-fibrous constituents will be removed from the fibers with substantial completeness. without, however, injuring the libcrs themselves to any material degree.

in addition to sullitc, alkali and resinous or other encrusting and non-fibrous constituents, the liquor frequently contains sodium carbonate and some sodium acetate, sodium resinates and some sodium sulpho-organic compounds. The liquor may contain soaps or materials of a similar character resulting from the combination of the sodium sulfite or caustic soda or both with saponifiable constituents of the wood treated, particularly in the case of resinous woods where resin soaps or compounds of a similar character may be formed in considerable amounts. It may also contain tanning material, dyes and other dissolved organic material.

The residual liquor is'usually mahogany in color, but the color varies somewhat in intensity with dii'l'erent Woods and is some what darker when small amounts of caustic are used. In reaction the liquor is alkaline to litmus but not strongly alkaline unless caustic has been employed, the degree of alkalinity obviously depending upon the amount of caustic used.

In consistency the residual liquor may be thinner than black liquors commonly obtained by soda and sulfate processes, and it may contain a smaller proportion of solids in solution because the cellulose is not attacked and dissolved by sodium sultite to any great extent. during the pulp-making operation.

Ono purpose of the present invention is the recovery of valuable constituents of the residual liquor, particularly the suliite radical and sodium content, so that these are consequently made available for the treatment of further quantities of wood.

According to the present invention, the residual liquor is treated in a relatively simple manner for the recovery of the more important constituents while the organic mate rials are destroyed. The residual liquor may thus be evaporated to dryness and the solids may be calcined or burned to produce sodium carbonate together with more or less sodium sullite, etc. These compounds may then be dissolved from the insoluble carbon and treated with sulfur dioxide or sodium bisul- La-J lite or both to eliminate carbon dioxide. product containing sodium sullite or a mixture of sodium sullite and sodium bisull'ite may thus be obtained. Alternatively, some of the carbonate may be converted into caustic soda and used such by addition thereof to the sodium sulfite liquor when a caustic liquor is needed.

lVhen the residual liquor from the cooking of wood with sodium mono-suliite or a miture containing a preponderating amount of sodium monosuliite and a smaller amount of caustic soda is calcined, for example, in a rotary furnace such as is used in the calcinetion of the concentrated residual liquors of the ordinary soda process, a considerable decomposition of the sodium sullite or sulfurous acid combinations contained in the liquors and in the dried product undergoing calcinetion, takes place, and a considerable amount of sulfur compounds escapes with the gaseous products of combustion by which the rotary calcining furnace is heated. In such cases the calcined product will contain a relatively large amount of sodium carbonate while it may still contain varying amounts of sodium sultite. This method of forming sodium carbonate forms the subject of our application Serial No. 513,161, liled llovcm her 5, 1921.

When the calcined product is leached to give a solution containing sodium carbonate and varying amounts of sodium sullite, this liquor may advantageously be used for recovering sulfur dioxide from the gases of the calcination. The gases from the rotary calcining furnace can, for example, be passed through an absorption tower through which the solution is passed, this absorption tower being arranged between the rotary calcining furnaces and the stack, and the necessary draft and circulation of the gases being secured by means of a fan. By using a tower or series of towe s in this way, the sulfur dioxide of the escaping gases can be recovered. for reuse in the process.

It is an advantage of this method of 1c generating the sodium suliite that it permits the use of ordinary calciningfurnaces such as are available in pulp mills operating according to the ordinary soda process, and requires merely the insertion of absorption towers and circulating fans between the rotary furnaces and the stack, and the circulation of the leach liquors through the absorption towers. The treatment of the residual liquors can otherwise be carried out in the same apparatus and with similar manipulation as in the ordinary soda process, although the procedure with the. residual liquors, according to the present invention, will have an entirely dilie 'entresult owing to the inherent differences in the residual liquor itself and in the reactions which take place during its treatment. The treatn'ient of 1,702,.esc

the residual liquors, in the manner described, results in the recovery of the greater part of the sodium content as well as of the sulfur dioxide content in the form of sodium sultite in solution available for further use in the cooking operation.

The .residual liquors produced from the cooking of dense hard woods (for example, birch, beech and maple) may have a radi caliy increased content both of organic constituents and of inorganic matter, such as combined sodium organic compounds anl sulfo-organie compounds. Residual liquors of such increased concentration will be somewhat diluted by admixture with wash waters, but dilution to an objectionable de ree can be readily prevented, and the treatment of the more concentrator liquors presents added advantage because of the decreased amount of water to be rcmvoed and the radically increased concentration of the constituents which the liquor contains.

The regenerative process of the present invention permits of making the pulp process a cyclic operation in which sodium sul'litc, with or without caustic soda, is employed as a cooking liquor in the production of pulp, with regeneration of the chemicals for furtl'acr use in the cyclic process. In carrying out the cyclic operation, the cooking the wood chi 38 can be carried out, for xample, in the manner more fully described in our prior application, Serial l lo. 481,14l7, filed June 28, 1921. When the pulp making procof said appli ation is combined ith the regeneration of the cooking liquor, or of ingredients of the cooking liquor, from the residual liquors, in the manner hereinbefore described, the pulp making process becomes a regenerative pulp prm-ess of a particularly advantageous character, enabling the pulp mill to operate with the treati ent of the residue liquors and the regeneration of the cooking liquors in a particularly advznlagcous manner.

The in s of sodium can be made up by adding: sodium carbonate or soda-ash and combining it with sulfur dioxide. The sulfur dioxide can be supplied to the necessary extent by simple sulfur burners and by absorption of the gases in alkaline solutions either of soda-ash or of residual liquors, or of leach liquors resiiilting from the calcination operations above described. amount of rue. sodium sullite or of sodium sullite an l caustic soda regenerated from the residual liquors can l e supplemented by the necessary additions to give a new cooking liquor suitable for further use in the process.

The regenerative or cyclic process of pulp manufacture, accordingly, presents important advantages in the manufacture of the pulp itself as forth more fully in our said prior application as well in the treatmentof the residual liquors in the manner herein described. lVe do not, however, claim the regenerative pulp process in the present application inasmuch as this forms the subject matter of a separate application.

It will thus be seen that the presentinvention provides an improved process of treating residual liquors for the recovery therefrom of a cooking liquor containing mainly sodium sulfite, either with or without caustic soda, and either with or without varying amounts of other sodium salts. This process involves the concentration of the residual liquors and the calcination of the concentrated product. The calcination is carried out under such conditions hat a considerable decomposition of the sodium sullite or sulfurous acid combinations contained in the liquors and in the dried products undergoing calcination takes place, and a considerable amount of sulfur compound escapes with the gaseous products of combustion from the calcining furnace. The calcined product, accordingly, will contain a relatively large amount of sodium corbonate, while it may nevertheless still contain *arying and appreciable amounts of sodium sullite. This product, when leached, will give a solution containing sodium carbonate and varying amounts of sodium sulfite. To the extent that the sodium sullite is thus directly recovered, the production of further amounts of sodium sulfite obviated. The gases given oil during the calcination will contain considerable amounts of sulfur dioxide, as above pointed out, and the solution leached from the calcined product may advantageously be used for recovering sulfur dioxide from such gases of the calcination. In this way, a considerable amount of sulfur dioxide can be recovered in the form of sodium sulfite for reuse. This recovery of sodium sullite for reuse thus involves a concentration and calcinatiou oi? the constituents of the residual liquor, with driving ol'l ot a considerable amount of sulfur dioxide therefrom during the calcinatiou, but with retention of part of the sulfur dioxide as sodium sullite in the calcined product, and the recovery of sulfur dioxide from the ei-scaping during the calcination in the solution leached from the calcined product.

This recovery process, in which the sultite radical of the sodium sulfite initially employed is recovered in part directly as sodium sullite from the calcined product, and in part by absorbing sulfur dioxide from the calcinetion gases in the solution leached from the calcined product, enables the rotary calcining furnaces of the ordinary soda process to be employed with simple additional equipment for the scrubbiu of the gases with the leached liquor to recover sulfur dioxide as sodium sullite.

In order to make up for losses of sulfur dioxide, sulfur dioxide from another source may be used for treating the solution leached from the calcined product; or sodium bisullite can be used, in which case additional sodium will also be supplied. Ihe treatment of the leached liquor with sulfur dioxide or with sodium bisullite will result in decomposing most or all of the sodium carbonate, setting free and d riving oll carbon dioxide, and forming sodium sultitc.

ll here the composite liquor is to contain caustic soda as well sodium sulfite, some of the sodium carbonate may. as above stated, he muzsticized and converted into caustic soda and used as such by addition thereof to the sodium sullil'e liquor otherwise regenerated or produced.

iii) invention may also be used with residual liquor which results from cooking wood with a cooking liquor containing sodium bisultitc.

This application contains subject matter disclosed in our co-pending applications Serial No. 513,761 and tierial No. 534,788, the latter having issued as Patent No. 1,637,515.

We claim:

1. The method of producing a cooking liquor from the residual liquor resulting; from the cooking of wood with a cooking liquor containing essentially sodium sulfite or sodium sulfite and caustic alkali, which comprises evaporating such liquor to dryness, calcining the dried product under conditions to drive sulfur compounds therefrom and to give a calcined product containing a relatively large amount of sodium carbonate, and also contail'iingsome sodium sullite, leaching the calcined product, and sulliting the same to convert sodium carbonate to sodium sulfite.

2. The method of treating residual liquor from the production of pulp with a cooking' liquor containing sodium sulfite or sodium sullite and caustic soda, which comprises evaporating the residual liquor to drymess, calcining the dry product without smelting the same, dissolving the sodium salts from the calcined product, and subjecting; the solution to the action of the suliite radical to convert sodium carbonate into sodium sullite.

3. The method of treating residual liquor from the production of pulp with a cooking liquor containingsodium sultite or sodium sulfite and caustic soda, which comprises evaporating the residual liquor to dryness, and subjecting the same to calciuatien under conditions to drive oil sulfur compounds therefrom and to give a calcined product con taining a relatively large amount of sodium carbonate and also containing sodium su-ltite.

4. The process of producing a cooking iquor containing sodium sullite which comprises digesting Wood with a cooking liquor containing essentially sodium sulfite or sodium sulfite and caustic soda, separating the resulting liquor from the cooked wood, concentrating the resultin 5. The method of producing a cooking; lie uor containing caustic soda, sodnui sul and sodium thiosul'liate, vhich compris evaporating a residual liquor from the cool:- ing of Wood with a cooking;- liquor containing; caustic sod: and sodium f'wl'lllllit calcin' comrentrated product 'u'ithout sliPll'lH give a calcined pl'fitlllCll containing; so carbonate and sodiiuirsultur coinoound eluding three elementcomgouiuls,

the calcined product, and treat liquor to convert part of the sodi m ate into caustic soda and to form lite.

6. The method of producing a cool i" nor from the residual liquor resul the cooking of Wood with coo containing essentially sodium or 50- dium sulfite and caustic alkali which coniprises evaporating; such liquor to dryness, ialcining the dried product under cond ions to drive sulfur COIilPOUIUlS the i rom i give a calcined product containing a tively large amount of sodium carbonate also containing some the calcined product, an subjecting the leach liquor in part to causticizii hf to convert sodium carbonate into caustic soda and in part to sultiting to convert sodi :n carhonatc into sodium sulfite.

7. The method of treating residual liquiir from the production of pulp with a cooking liquor containing sodium suliite or sodium sulfite and caustic soda which compri evlporatiim; the residual liquor to rhyme calcining the dry product in a Furnace under conditions to Form sull'ur dioxi-zle the; and to give a alcined product contuh .i p; a relatively large amount oi? sodium (illl)()l'1:l,il\ leaching the calcined product, and ahsorhi the sulfur di(7 idc liornwd during}; the cination in such solution.

8. The method oltrcatinp; residual liquor from the, production of pulp with a cooking; liquor containing; sodium sultitc sodii sulfite and caustic soda, which comprises evaporating; theresidual liruior to calcining the dry product in furnace conditions to form sulfur dioxide than and to give a calcined product contai relatively la no amount of sodium carh absorbing; the sulfur dioxide torzueo diu' honate and thereby forming sodium for further use in the coolnn liquor.

9. The process of PITOtl'llClIlf cooking; liqcontaining: essentially sodium sultite or sodium suliite and caustic soda, separating the resulting liquor from the cooked Wooch concentrating the resulting liquor, subjectin the trateiil liquor to 'alci 'on u'thout the saint; efiiiractir he calcined promica and treating the resultii'ig" solution co part with sultur tiI5"" Q or a compound l to convert sou sullite, and in w li e rad duun ca port by ca Wits lime to term 61:115- tic soda lllh il liqa cool;-

iih' i1 cum: to :miuct nituout tha sod um ,"o 'uluct, and $41103 1;-

tion oi? the sullite curlionate into a and sodium hi- I uul liquor .n'nises evaporating the i 'ness, suhgcctmg; the d1 operation undcz with (ho ruicompounds ace gases SLZl'ICIGl t quntit to are a l'urnace product containing" a i l- Oflll in carbonate and (luau-sulfur compounds 7' fun ice product tor the production of a cool:-

i 1 inc; liquor cont mine sul lite ot' scdiuuu the so d1 1 a content ct such sullite being derived in 1 part from such sodium-sulfur compounds and in part from the carhonate of sodium.

In a process for regenerating cooking; nor, the steps which include dige ting ee iuo; material by means oi cooking); ides a suhiuiantiai amount oi l which incl: a ltilc o'i" an allmli-nielal and ci'mtinuiug the digesting treatment until tihres thercot are rcadil o urahlc from each other by me- (llilllli'ill treatment, separation; resulting: residual liquor from resu ting tihrous 1 :ateriuh In a process for regenerating cooking liquor, the steps which include digesting" cellulose-li-aring miterial by means cl cool-tiug liquor which includes a substantial amount of a suli'ite of an alkali-metal and continuing the digesting" treatment until fibres thereof are rearily separable from each other by mechanical treatment, separating resulting residual liquor from resulting fibrous material, removing water from residual liquor, furnacing the residue under conditions adapted to yield a furnace product including a preponderating amount of ulkili-metal carbonate and a lesser amount oi ulkali-metal sulfur-bearing couqiouuds, and forming a cooking liquor including a sultite of an alkali-metal the allmii-metal content t such suliite being derived in part from such alkali-metal carbonate and in part from such alkali-metal sulfur-bearing compounds.

14-. The method of treating residual liquor from the. production of pulp with a cooking liquor containing a sultite oi sodium, which comprises evaporating the residual liquor to dryness, burning the organic matter therein, forming a solution containing sodium salts derived from the resulting product, said sodium salts including a carbonate o 1 sodium and a sodium-sult'ur compound. and subjecting the solution to the :1 -tion of sult'ur dioxide by passing the solution over a tower and passing sull ur-dioxidebea ring gases through the tower to absorb sul'liur-dioxide in the liquor.

15. In a process for regenerating a cooking liquor, the steps which include digesting wood by means of a cooking liquor supplied with about to et0% of sodium monosullite tlla SO based on the airdried weight of the wood, and digesting until the wood fibres are substantially freed from non-it brous constituents, separating resulting residual liquor from resulting fibrous material, rcmoving water from such residual liquor furnacing the residue under conditions adapted to form furnace gases which carry the greater amount of the sulfur present in such cooking liquor as sodium monosullite hen charged into the digester and under conditions adapted to yield a furnace product including sod ium compounds of which a preponderating amount is sodium carbonate and a lesser amount is sodium-sulfur compounds. forming therefrom a cooking liquor including sul tite of sodium derived from sodium compounds contained in such furnace product, the sodium content of such cooking liquor being derived in part from a carbonate of sodiuni and in part from the sodium-sulfur compounds.

16. The method of treating residual liquor "from the production of pulp with a cooking liquor containing a sultitc of sodium which comprises evaporating the residual liquor to dryness, subjecting the dry material to a furnacing .)perat-ion under conditions to drive off sulfur compounds with the furnace gases in suilieient quantity to give a furnace product containing a relatively large amount of so dium carl'mnate and also containing sodiumsultur compounds and treating such furnace product by means of a sultite radical for the production of a cooking liquor containing sull'ite of sodium, the sodium content of such sullite being derived in part from such sodium-sul'l ur LUlllPOlllltlS and in part from the carbonate of sodium, the treatment of the sullite radiial being continued until substan tially all of the carbonate of sodium has reacted therewith.

17. The method of treating residual liquor from the production of pulp with a cooking liquor containing a sulfite of sodium which comprises evaporating the residual liquor to dryno subjecting the dry material to a furnacing operation under conditions to drive oil sulfur compounds with the furnace gases in sufticientquantity to give a furnace product containing a relatively large amount oi sodium carbonate and also containing sodiumsul'tur compounds and treating such furnace product by means of a sulfite radical recovered from the iurnacing operation tor the production of a cooking liquor containing sultitc of sodium, the sodium content of such sultite being derived in part from such sodium-sul't'ur compounds and in part from the carbonate of sodium.

In testimony whereof we aflix our signatures.

LINN BRADLEY. EDWARD P. MGKEEFE. 

